The present invention relates to subranging analogue to digital converters.
A known subranging analogue to digital converter comprises a first analogue to digital converter for receiving an analogue input signal to be converted, connected in series to a digital to analogue converter the output of which is connected in series via an operational amplifier to the input of a second analogue to digital converter. One of the inputs of the operational amplifier is connected to the output of the digital to analogue converter and a second input of the operational amplifier is connected via a delay line to the input of the first analogue to digital converter. In operation, the operational amplifier subtracts the analogue input signal from the output of the digital to analogue converter to provide an "error" signal which is transmitted to the input of the second analogue to digital converter. At least a part of the digital output from the second analogue to digital converter is combined with the digital output from the first analogue to digital converter to provide the digital output signal of the subranging analogue to digital converter.
The speed and accuracy of convertion of the analogue input signal to the digital output signal in the above described subranging circuit is adversely affected by signal propagation delays within the digital to analogue converter and within the series connected operational amplifier. These two propagation delays act as a constraint on the frequency of operation and performance of the subranging circuit.